The alterations in design of a Wilson‐Blackett automatic cloud‐chamber apparatus, found necessary or convenient in adapting it to photographing tracks of high‐speed ions from a high‐voltage tube, are briefly described. An experimental cloud‐chamber, which can be oriented in any position, constructed from a six‐inch diameter metallic sylphon‐bellows, free from leaks and with several other advantages, is shown. A convenient type of mercury spark‐lamp which makes possible the use of fine‐grained positive‐emulsion films is described. Designs are given for a larger sylphon‐type chamber based on the satisfactory experience with the smaller chamber.

Based on observations of thermoelectric power and the Wiedemann‐Franz ratio λ/κ, a compensated radiation thermopile has been built and operated in a vacuum at low temperatures, which shows a more than tenfold increase in sensitivity when operated at the temperature of liquid oxygen, as compared to operation at 25°C.

By splitting the graphiteresistor tube of a vertical, evacuated, high temperature furnace, the construction is simplified, the possibility of resistor breakage is circumvented and the zone of highest temperature is brought deeper in the furnace than in the spiral or solid tube types of vertical furnace. The construction of the furnace cover permits crucibles to be put in or removed from the furnace without breaking the main vacuum seal. The melt can be observed visually, or the gases from the melt can be drawn off to other apparatus, without having to pass through the main furnace volume. The furnace reaches 2000°C on 7 kw of power input.

A detailed technique is described for the measurement of the permeability of porous media, by the use of either liquids or gases. Derivations are given of the formulae by which the permeability may be computed from the laboratory measurements. In addition to defining a convenient permeability unit, it is proposed to call it the ``darcy.'' Field measurements on the effective permeability of underground sands are discussed, and the appropriate formulae are derived. These include expressions for liquidflow, gas flow, gravity flow and composite artesian and gravity flow. Correction curves are given for application when the wells do not completely penetrate the producing sands.